GTP-binding protein (G protein) is a generic name of endogenous protein group having an activity of hydrolyzing GTP, and has been known for a G protein group involved in mRNA translation, a trimer G protein group conjugated with 7-times transmembrane receptor, a low-molecular-weight G protein group (“Experimental Medical Science,”21:137-145, 2003) and the like. Among these groups, 100 or more kinds of low-molecular-weight G protein proteins have been reported as proteins having molecular weights of 20,000 to 30,000 with no subunit structure, and after isoprenylation, these proteins transfer to cell membranes to participate in intracellular signal transmission as GTP-bound form (on)/GDP-bound form (off).
The low-molecular-weight G protein group is further divided into five super-families, that is, Ras, Rho, Rab, Arf and Ran (Physiol. Rev., 81:153-208, 2001). Among these families, the Rho family is further divided into subfamilies such as Rho, Rac, Cdc42. The Rho family regulates cellular functions via re-organization of an actin cytoskeleton, and similarly to the Ras family, participates in gene expression. Rho induces formation of actin stress fiber or focal contact, Rac induces formation of lamellipodia, and Cdc42 induces formation of filopodia.
Specifically, Rac protein (also referred to as Rac1) is a protein consisting of about 200 amino acids and has a structure similar to that of Rho, but regulates an actin cytoskeleton in a mode different from that of Rho. Rac protein is also reported to activate JNK/p38 and NF-κB.
On one hand, an HMG-CoA
(3-hydroxy-3-methyl-glutaryl-CoA) reductase inhibitor is an inhibitor of an enzyme catalyzing conversion of HMG-CoA into mevalonic acid in an early rate-determining stage in biosynthesis of cholesterol, and is known as a hypercholesterolemia remedy. The HMG-CoA reductase inhibitor has been verified to reduce the onset of arteriosclerosis in a large-scale test, and from overlap analysis or the like, it has been revealed that this reduction of the onset is responsible for HMG-CoA reductase inhibitor's action in a vascular wall, aside from its action of reducing cholesterol by inhibiting HMG-CoA reductase in the liver.
That is, it is believed that the HMG-CoA reductase inhibitor inhibits HMG-CoA reductase in cells of a vascular wall, and via its action of reducing the formation of isoprenoid, reduces the activity of low-molecular-weight G protein, thus exerting various influences on cellular functions to exhibit anti-inflammatory reaction in the vascular wall thereby suppressing arteriosclerosis.
Further, the HMG-CoA reductase inhibitor has actions such as suppression of endothelial cell activation, improvement of endothelial functions, suppression or improvement of adhesion or foaming of monocytes/macrophages, suppression of migration/proliferation of smooth muscles, and stabilization of plaques, and Rho, Rac, and Cdc42 that are low-molecular-weight G proteins in the Rho subfamily are reported to participate in these actions. Particularly, the effect of the HMG-CoA reductase inhibitor on improvement of endothelial functions appears evidently in a short time after administration, and is considered important among the various actions.
Recently, it is revealed that Rac participates in signal transmission mediated by angiotensin II, PDGF, thrombin, endothelin, leukotriene B4 and the like in vascular walls and promotes the activity of NADPH, thus playing an important role in the progress of a vascular disease (Am. J. Physiol. Cell Physiol., 285:C723-734, 2003), and it is reported that Cdc42 also participates in proliferation of vascular endothelial cells and in recovery of barrier functions (J. Cell Sci., 114:1343-55, 2001; J. Biol. Chem., 277:4003-9., 2002; Circ. Res., 94:159-166, 2004) and also in signal transmission of endothelin (J. Biol. Chem., 278:29890-900, 2003).
Further, the present inventors examined the influence of pitavastatin as HMG-CoA reductase inhibitor on gene expression in vascular endothelial cells, and they found that pitavastatin suppresses expression of inflammatory cytokine IL-8 or MCP-1, expression of endothelin and expression of PAI-1, promotes expression of NO synthase involved in vascular expansion and shrinkage, expression of thrombomodulin in a coagulation and fibrinolysis system (J. Atheroscler. Thromb., 9:178-183, 2002), and suppresses expression of PTX3 (promoting expression of TF and serving as an indicator of progress of arteriosclerosis) (J. Atheroscler. Thromb., 11:62-72, 2004).